Simultaneous dual mode operation in cellular networks

ABSTRACT

Embodiments of the present invention provide for determining whether an insufficient guard band exists in a spectrum carrying potentially interfering signals and allocating a temporary guard band to spectrally separate the two signals, thereby reducing or preventing inter-signal interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to communication systems and more particularly to guard bands between a first mode and a second mode of communication.

2. Description of the Related Art

Wireless service providers are often provided one or more blocks of spectrum. Often one block of spectrum neighbors another block of spectrum carrying a different signal type. In some circumstances, a signal at one end of a block of spectrum may be interfered by a signal of the different type from a neighboring block of spectrum. For example, the different signal time may be transmitted with a much higher power. If the higher power signal spills over into the adjacent band, reception of signals within the band may be hampered.

One solution to reduce interference between signals from neighboring blocks of spectrum is for a permanent guard band to be placed at one end or both ends of a block of spectrum. The permanent guard band spectrally separates signals from possibly interfering signals from other bands.

Therefore, a need exists to more efficiently temporarily allocate a guard bands when an interfering signal may be present, thereby both reducing inter-band interference. Furthermore, a need exist to free the allocated guard bend when no interfering signal is expected, thereby more optimally using spectrum where the guard band would otherwise exist.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide for determining whether an insufficient guard band exists in a spectrum carrying potentially interfering signals and allocating a temporary guard band to spectrally separate the two signals, thereby reducing or preventing inter-signal interference.

Some embodiments of the present invention provide for a system for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the system comprising: a memory; a processor coupled to the memory; and program code executable on the processor, the program code operable for: receiving the first signal in the first mode from a user equipment (UE); determining that the UE requests operation in the second mode; and determining whether an insufficient guard band exists. In some embodiments, the first mode comprises time division duplex (TDD) operation and the second mode comprise frequency division duplex (FDD) operation.

Other embodiments of the present invention provide for a method for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the method comprising: receiving the first signal in the first mode from a user equipment (UE); determining that the UE requests operation in the second mode; and determining whether an insufficient guard band exists. In some embodiments, the first mode comprises time division duplex (TDD) operation and the second mode comprises frequency division duplex (FDD) operation.

Some embodiments further comprise creating a guard band if the insufficient guard band exists. In some alternative embodiments, the guard band comprises a bandwidth that falls at least partially within a first band operating in the first mode, or a bandwidth that falls at least partially within a second band operating in the second mode, or a bandwidth that falls partially within a first band operating in the first mode and falls partially within a second band operating in the second mode. In some embodiments, creating a guard band comprises reconfiguring one or more transmitters to limit transitions within the guard band.

In some embodiments, receiving the first signal comprises receiving a first message sent from the UE; and determining that the UE requests operation in the second mode comprises determining from the first message that the UE requests operation in the second mode. In some embodiments, the received message from the UE comprises a request for a service, such as a broadcast service, or an explicit request for dual-mode operation, or an implicit request for dual-mode operation. Some embodiments further comprise sending, to a UE, a request for an indication from the UE of a sufficient guard band bandwidth; and/or receiving an indication from the UE of a sufficient guard band bandwidth; and/or sending, to a UE, one or more parameters indicative of a service provided in the second mode. In some embodiments, at least one of the one or more parameters comprises an encryption parameter.

Some embodiments of the present invention provide for a computer program product comprising program code for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the computer program product comprising program code for: receiving the first signal in the first mode from a user equipment (UE); determining that the UE requests operation in the second mode; and determining whether an insufficient guard band exists.

Some embodiments of the present invention provide for user equipment (UE) for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the UE comprising: a memory; a processor coupled to the memory; a transmission system operable to communicate contemporaneously using the first signal operating in the first mode and the second signal operating in the second mode; and program code executable on the processor, the program code operable for: sending the first signal in the first mode from the UE to a network; and indicating to the network that the UE requests operation in the second mode.

Some embodiments of the present invention provide for a method of using user equipment (UE) for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the method comprising: sending the first signal in the first mode from the UE to a network; indicating to the network that the UE requests operation in the second mode; and communicating contemporaneously using the first signal operating in the first mode and the second signal operating in the second mode. In some embodiments, the first mode comprises time division duplex (TDD) operation and the second mode comprises frequency division duplex (FDD) operation. In some embodiments, communicating contemporaneously comprises receiving and processing a broadcast signal in the second mode while communicating signals in the first mode.

Other features and aspects of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features in accordance with embodiments of the invention. The summary is not intended to limit the scope of the invention, which is defined solely by the claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a UE located in overlapping coverage areas provided by one or two Node Bs.

FIG. 2 illustrates first mode and second mode signals within a spectrum.

FIGS. 3A and 3B illustrate contiguous and non-contiguous allocated bands.

FIGS. 4A, 4B and 4C show various positions of a guard band within allocated bands in accordance with the present invention.

FIG. 5 illustrates first mode and second mode signals separated by a guard band in accordance with the present invention.

FIGS. 6A, 6B, 6C and 6D illustrate signaling between a UE and a Node B in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, reference is made to the accompanying drawings which illustrate several embodiments of the present invention. It is understood that other embodiments may be utilized and mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of the present disclosure. The following detailed description is not to be taken in a limiting sense, and the scope of the embodiments of the present invention is defined only by the claims of the issued patent.

Embodiments of the present invention provide for determining whether an insufficient guard band exists in a spectrum carrying potentially interfering signals and allocating a temporary guard band to spectrally separate the two signals, thereby reducing or preventing inter-signal interference. Some embodiments provide for systems communicating band allocations near a band edge. The system may be integrated with a neighboring system to provide improved control. Communication may be initiated by User Equipment and/or by a base station. Some embodiments provide for systems reallocating an active user to spectrum away from a band edge. Some embodiments, a User Equipment and/or a Node B determine whether an interfering signal exists.

Some portions of the detailed description which follows are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that can be performed on computer memory. A procedure, computer executed step, logic block, process, etc., are here conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those utilizing physical manipulations of physical quantities. These quantities can take the form of electrical, magnetic, or radio signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. These signals may be referred to at times as bits, values, elements, symbols, characters, terms, numbers, or the like. Each step may be performed by hardware, software, firmware, or combinations thereof.

A wireless communication system usually include both user elements and network elements. Such wireless communication systems include GSM, 3^(rd) Generation Partnership Program (3GPP), and IEEE 802.11 systems, and the like. A user element, such as User Equipment (UE) in a 3GPP system, wirelessly communicates with one or more network elements, such as a Node B in a 3GPP system. Such wireless communication systems may include one or more UEs and/or one or more Node Bs.

Herein, a UE, mobile, cellular unit, cell phone, terminal and the like associated with such a wireless system may be referred to as User Equipment or a UE. UEs are typically but not necessarily mobile units having battery supplied power. Alternatively, a UE may be a fix device obtaining power from a power grid. A UE may include memory, a processor and program code executable on the processor. The memory and/or the processor and/or the program code may be combined into a silicon structure. For example, a processor may include a dedicated processor, a form of built-in RAM and program code saved in a form of ROM.

Similarly, herein, network elements such as a Node B, base station (BS), base transceiver station (BTS), base station system/subsystem (BSS), or the like may be referred to as a Node B. Network elements may also include elements such as a base station controller (BSC), mobile switching center (MSC), and the like.

FIGS. 1A and 1B illustrate a UE located in overlapping coverage areas provided by one or two Node Bs. As shown in FIG. 1A, a Node B 100 may provide two communication mode signals (110, 120) having overlapping footprints. Alternatively, two Node Bs may be co-located, thus providing an equivalent overlapping coverage area. In FIG. 1B, two Node Bs (100A, 100B) are geographically separated, however, the pair of Node Bs provide respective mode signals (110, 120) similarly resulting in an overlapping coverage area.

At times, a UE 130 may be positioned as shown in an overlapping coverage area. The one or more Node Bs 100 resulting in an overlapping footprint may provide multiple modes of operation. For example, a first mode of operation may be a Time Division Duplex-Code Division Multiple Access (TDD-CDMA) mode and a second mode of operation may be a Frequency Division Duplex-CDMA (FDD-CDMA) mode. Alternatively, a first mode of operation may operate in an FDD-CDMA mode and a second mode of operation may operate in a TDD-CDMA mode. Alternatively, a first mode of operation may operate in a frequency division multiple access (FDMA) mode and a second mode of operation may operate in a TDD-CDMA mode. Those skilled in the art will realize that other mode combinations are also possible.

Signaling provided in one mode of operation may allow for a service that another mode or other modes may not support. For example, a system operating using a FDD-CDMA mode may provide for efficient use of resources for point-to-point data traffic but a system operating using an TDD-CDMA mode may provide for more efficient use of resources for point-to-multi-point broadcast services. To more optimally utilize resources, a UE may begin communication with a first mode and subsequently may access service using the second mode.

Systems operating with separate communication modes may share an overlapping spectrum allocation. Alternatively, systems operating with two different modes may have non-overlapping spectrums, which may be separated by a large band used for other communications, or which may be separated by a small guard band to help reduce intersystem interference, or which may be share a common boundary.

FIG. 2 illustrates first mode and second mode signals within a spectrum. A band 200 allocated to a first mode and a band 300 allocated to a second mode are separated by a common boundary 400. A first system allocated to the first band 200 may include one or more distinct communication signals (210, 220). Similarly, a second system allocated to the second band 300 may include one or more distinct communication signals (310, 320). Neighboring signals may or may not be separated by an intra-band guard band (215, 315) or an inter-band guard band (404). FIG. 2 also shows a power spectral v. spectrum plot of two active signals (210, 310) having respective center frequencies (214, 314).

In the example shown in FIG. 2, the first signal 210 has a peak power 216 that is substantially less than a peak power 316 of the second signal 310. Even though the second signal is allocated spectrum only within the second band 300, the second signal 310 is shown to spill into the first band 200 and interfere with the first signal 210 as illustrated in region 406.

FIGS. 3A and 3B illustrate contiguous and non-contiguous allocated bands. A first band 200 provides for channels (210, 220, 230, 240) for a first mode of operation. Two bands (300, 301) provide for channels (310, 320, . . . , N₀ & 311, 321, . . . , N₁) for a second mode of operation. For example, band 200 may represent a band operating in a TDD-CDMA mode, and bands 300 and 301 may represent bands used for operating in a FDD-CDMA mode. Uplink and downlink communications may be separated by time and/or channel in the TDD band 200. In FDD-CDMA operation, band 300 may provide uplink channels and band 301 may provide corresponding downlink channels. As described above, bands may be adjacent or contiguous as shown in FIG. 3A at 400, or alternatively, may be separated by a guard band or spectrum as shown in FIG. 3A at 408.

FIGS. 4A, 4B and 4C show various positions of a guard band within allocated bands in accordance with the present invention. At or near a band delineation frequency (401, 402, 403), a signal at one end of an allocated band 300 may interfere with a signal at the close end of another allocated band 200 if no guard band exists or if a small guard band exists. In either case, an insufficient guard band may exist, thus allowing for the possibility of interference between signals from respective bands. If an insufficient guard band exists, a guard band may be created thus separating otherwise possibly interfering signals. The created guard band may reside entirely outside band 200 as shown at 501 to the right of 401 in FIG. 4A. Alternatively, the created guard band may reside entirely outside band 300 as shown at 502 to the left of 402 in FIG. 4B. Alternatively, the created guard band may reside partially inside both band 200 and band 300 as shown at 503 straddling 403 in FIG. 4C.

FIG. 5 illustrates first mode and second mode signals separated by a guard band in accordance with the present invention. The first signal 210 operating in a first mode and the second signal 310 operating in the second mode previously shown interfering in FIG. 2 are here shown separated by a guard band 500. For convenience, the three positions of a guard band (501, 502, 503) relative to the band delineation frequency (401, 402, 403) of FIGS. 4A-4C are shown combined on a single chart. The signals 210 and 310 continue to have relative peak power differences (216, 316) as before, however, the interference between the signals (210, 310) in region 406 (FIG. 2) has been significantly reduced as shown in region 407.

FIGS. 6A, 6B, 6C and 6D illustrate signaling between a UE and a Node B in accordance with the present invention. FIG. 6A shows an exchange between a UE 130 and a Node B 100. To initiate a request for service, a UE 130 sends the Node B 100 a request for dual mode service indication (request-dual-mode message 710). A request-dual-mode message 710 may be an explicit request for dual mode operation. For example, the UE 130 may precisely and clearly express an expectation for a resource in the second mode of operation if such a resource is available in the network. Alternatively, the request-dual-mode message 710 may be an implied request for dual mode operation. For example, the UE 130 may suggest that it may use a resource, if available, in the second mode of operation or may be a request for a service that is offered in the second mode of operation. In either case, the UE 130 may either be currently operating using the first mode of communications, or alternatively, the UE 130 may initiate operation in the request-dual-mode message 710 as a first message in the first mode.

Upon receiving request-dual-mode message 710, the Node B 100 and/or other network element(s) may determine that the UE 130 requests dual mode operation, either explicitly or implicitly. Alternatively, the Node B 100 and/or other network element(s) may infer that the UE 130 requests dual mode operation. For example, the Node B 100 or other network element(s) may determine based on information known by the network about a UE that the UE may use a resource in the second mode of operation, if available. Alternatively, the Node B 100 or other network element(s) may determine that dual mode operation is requested based on a type of request received from the UE 130. For example, the UE may request a service, such as to receive point-to-multipoint broadcast programming, that is offered in the second mode. In some embodiments, the network may determine that the UE 130 has the capability to function in dual mode prior to granting the request.

The Node B 100 and/or other network element(s) may determine whether or not an insufficient guard band exists. Having an insufficient guard band may allow interference between data communicated using the first mode and data communicated using the second mode. For example, a UE 130 may be exchanging data with the network using the first mode. A spectral resource neighboring the first mode signal may be available but may also be too close in frequency, thus leading to potential inter-signal interference. Similarly, a signal presently used by a different UE may be positioned in the spectrum such that it may interfere with the first mode signal of the UE 130, a second mode signal of the UE 130, or both.

If an insufficient guard band exists, the network may create a temporary guard band. The temporary guard band may fall at least partially within a first band operating in the first mode, or may fall at least partially within a second band operating in the second mode, or may fall partially within a first band operating in the first mode and falls partially within a second band operating in the second mode. In addition, creating a guard band may include reconfiguring one or more transmitters to limit transmissions within the temporary guard band. After the need for the temporary guard band has passed (e.g., dual mode operation has finished), the network may free the temporary guard band to allow the spectrum to be used to satisfy other requests.

If a resource is currently available for the UE 130 for use in the second mode of operation, the Node B 100 and/or other network element(s) may instruct the UE 130 to start dual mode operation (start-dual-mode message 720). Alternatively, if a resource can be made available for use in the second mode of operation, the Node B 100 and/or other network element(s) may instruct one or more UEs to reconfigure thereby making available the resource for UE 130, as described below with reference to FIG. 6D. The start-dual-mode message 720 may be an expressed instruction to begin dual mode operation. Alternately, the start-dual-mode message 720 may be a message granting a service, thus implying dual mode operation. For example, the message 720 may be a response to a request for a broadcast service (message 710). The message 720 may include information that the UE 130 may use to properly receive and process the requested broadcast service.

Upon receipt of the start-dual-mode message 720, the UE 130 determines, either explicitly or implicitly, that the UE may begin dual mode operation. Alternatively, the network may deny the UE's request explicitly (e.g., by sending the UE 130 a request-denied message (not shown)), or implicitly by not responding to the UE 130 dual-mode-request 710. In the later case, the UE 130 may time out and may send one or more additional request-dual-mode messages 710. Alternatively, the UE 130 may time out and may terminate its request for dual mode operation.

After receipt of start-dual-mode message 720, the UE 130 and Node B 100 may continue to communicate data in the first mode, as indicated by message(s) 800. Concurrently, the UE 130 and Node B 100 may begin to communication data in the second mode, as indicated by message(s) 900. Contemporaneous operation between the UE 130 and the network(s) in both first mode operation and second mode operation allows the UE 130 benefits of a service provided in the first mode and a service provided in the second mode over the same time period.

FIG. 6B shows an exchange of messages used to determine whether or not a UE 130 has one or more general or specific capabilities. In some embodiments, a Node B 100 sends a request to a UE 130 to determine its capabilities (UE-capability-request message 730). In response, the UE 130 may reply with its capabilities (UE-capability-response message 740). In other embodiments, the UE 130 may send capability information in an unsolicited message (not shown).

The solicited pair of messages (730, 740) or the unsolicited message (740) may occur at various points in an exchange of information between a UE 130 and a network. For example, in some embodiments capability information may be exchanged during an initial UE exchange with the network. In some embodiments, the capability information may be exchanged before or as part of a request-dual-mode message 710. In some embodiments, capability information may be exchanged either before or after a start-dual-mode message 720.

The capability information may be used by the network, for example, to determine a minimum bandwidth of a temporary guard band. Some UEs may include an input filter having a shaper frequency cut-off, thus allowing these UEs to have spectral resource allocated more closely together. As another example, capability information may inform a network whether or not a UE is enabled to operate with an encryption algorithm. As a further example, capability information may inform a network as to determine whether or not a UE has a concurrent dual-mode ability.

FIG. 6C shows an exchange of messages, as in FIG. 6A, with the network providing an additional set of information that a UE 130 may use to establish an encrypted link (e.g., encryption keys for service in the second mode). Encryption information may be provided to the UE 130 as part of a start-dual-mode message 720, or alternatively as a separate message 750, as shown.

FIG. 6D shows an exchange of messages that may be used to reconfigure a UE 131. The UE 131 may be a separate UE from the requesting UE 130 described above. Equally, the UE 131 may be the same UE 130 as describe above. For example, the UE 131 may be operating using a resource that the network determines it will reclaim in order to create a temporary guard band needed for dual mode operation of UE 130. The network may allocate a new resource for use by the UE 131, then send a message from the Node B 100 to the UE 131 to instruct the UE 131 to free the current resource and use the new resource. Thereby, a previously used resource may be free such that the network may create a temporary guard band for UE 130.

FIGS. 6E, 6F AND 6G illustrate signaling following a measurement by a UE 130. After a UE 130 performs a measurement of a current cell and/or one or more neighboring cells, the UE 130 may report this measurement information to the network. A UE 130 may report measurement information to a network along with another message, as shown in FIG. 6E. FIG. 6E shows a UE 130 requesting a dual mode service, as described above with reference to message 710, however, the request-dual-mode message 715 includes measurement report information. Alternatively, the measurement information may be reported to the network in a dedicated measurement reporting message 780, as shown in FIG. 6F.

Alternatively, a UE 130 may use results from one or more measurement to determine that a specific action should be requested. For example, FIG. 6G shows a UE 130 taking measurements of a current cell and/or one or more neighboring cells. Based on the measurement(s), the UE 130 determines to send a request for reconfiguration (request-reconfiguration message 790). For example, if the UE 130 determines that a second signal is interfering with either the UE's first mode signal or the UE's second mode signal, the UE can request a reconfiguration of UEs and resources to alleviate the interference. Upon receiving the request-reconfiguration message 790 by the Node B 100, the network may determine that a reconfiguration of resources would benefit system performance or the like. The network may reallocate a UE 131 (as shown in FIG. 6D) or may reallocate the UE 130 as shown by a response message from the Node B 100 (response message 795).

While the invention has been described in terms of particular embodiments and illustrative figures, those of ordinary skill in the art will recognize that the invention is not limited to the embodiments or figures described. For example, many of the embodiments described above are described with reference to TDD-CDMA and FDD-CDMA standards, however, the present invention is also applicable to other wireless networks. Furthermore, embodiments are not limited to wireless links. For example, the present invention is applicable to wired links, such as coaxial cable, twisted pairs, and optical cable, as may be appreciated by those skilled in the art.

The figures provided are merely representational and may not be drawn to scale. Certain proportions thereof may be exaggerated, while others may be minimized. The figures are intended to illustrate various implementations of the invention that can be understood and appropriately carried out by those of ordinary skill in the art. Therefore, it should be understood that the invention can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration and that the invention be limited only by the claims and the equivalents thereof. 

1: A system for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the system comprising: a memory; a processor coupled to the memory; and program code executable on the processor, the program code operable for: receiving the first signal in the first mode from a user equipment (UE); determining that the UE requests operation in the second mode; and determining whether an insufficient guard band exists. 2: The system of claim 1, wherein the first mode comprises time division duplex (TDD) operation and the second mode comprises frequency division duplex (FDD) operation. 3: A method for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the method comprising: receiving the first signal in the first mode from a user equipment (UE); determining that the UE requests operation in the second mode; and determining whether an insufficient guard band exists. 4: The method of claim 3, wherein the first mode comprises time division duplex (TDD) operation and the second mode comprises frequency division duplex (FDD) operation. 5: The method of claim 3, further comprising creating a guard band if the insufficient guard band exists. 6: The method of claim 5, wherein the guard band comprises a bandwidth that falls at least partially within a first band operating in the first mode. 7: The method of claim 5, wherein the guard band comprises a bandwidth that falls at least partially within a second band operating in the second mode. 8: The method of claim 5, wherein the guard band comprises a bandwidth that falls partially within a first band operating in the first mode and falls partially within a second band operating in the second mode.
 9. The method of claim 5, wherein creating a guard band comprises reconfiguring one or more transmitters to limit transmissions within the guard band. 10: The method of claim 3, wherein: receiving the first signal comprises receiving a first message sent from the UE; and determining at the UE requests operation in the second mode comprises determining from the first message that the UE requests operation in the second mode. 11: The method of claim 10, wherein the received message from the UE comprises a request for a service. 12: The method of claim 11, wherein the service comprises a broadcast service. 13: The method of claim 10, wherein the received message from the UE comprises an explicit request for dual-mode operation. 14: The method of claim 11, wherein the received message from the UE comprises an implicit request for dual-mode operation. 15: The method of claim 3, further comprising sending, to a UE, a request for an indication from the UE of a sufficient guard band bandwidth. 16: The method of claim 3, further comprising receiving an indication from the UE of a sufficient guard band bandwidth. 17: The method of claim 3, further comprising sending, to a UE, one or more parameters indicative of a service provided in the second mode. 18: The method of claim 17, wherein at least one of the one or more parameters comprises an encryption parameter. 19: A computer program product comprising program code for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the computer program product comprising program code for: receiving the first signal in the first mode from a user equipment (UE); determining that the UE requests operation in the second made; and determining whether an insufficient guard band exists. 20: User equipment (UE) for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the UE comprising: a memory; a processor coupled to the memory; a transmission system operable to communicate contemporaneously using the first signal operating in the first mode and the second signal operating in the second mode; and program code executable on the processor, the program code operable for: sending the first signal in the first mode from the UE to a network; and indicating to the network that the UE requests operation in the second mode. 21: A method of using user equipment (UE) for communicating using a first signal operating in a first mode and a second signal operating in a second mode, the method comprising: sending the first signal in the first mode from the UE to a network; indicating to the network that the UE requests operation in the second mode; and communicating contemporaneously using the first signal operating in the first mode and the second signal operating in the second mode. 22: The method of claim 21, wherein the first mode comprises time division duplex (TDD) operation and the second mode comprises frequency division duplex (FDD) operation. 23: The method of claim 21, wherein communicating contemporaneously comprises receiving and processing a broadcast signal in the second mode while communicating signal in the first mode. 